1. Field
This disclosure relates to data storage on digital optical tape.
2. Description of the Related Art
Color photographic recording film is unsuitable for long-term archival storages of motion pictures and other imagery. Color film contains photographically active chemicals which remain in the film after development. These chemicals will continue to undergo chemical reactions which cumulatively cause color fading in the images.
Conventional magnetic recording media are typically produced using a continuous wet coating process, where a magnetic dispersion is applied to the base film. This magnetic dispersion consists of binders, magnetic pigments, dispersants and lubricants which are dissolved in organic solvents to form a slurry. These binders (along with residual solvent, dispersants, etc.) will, over time, undergo chemical processes which may weaken their ability to hold the magnetic pigments to the base media or may cause breakdown of the magnetic pigments themselves due to chemical reactions. Thus magnetic storage media may also be unsuitable for archival storage of images and other data.
Digital optical tape system (DOTS) recording medium based on a very stable, very sensitive phase-change recording material has a potential for archival storage of imagery, data, and documents for periods in excess of 100 years. It has been shown that DOTS recording medium is stable for 100 years at 38° C. and over 200 years at room temperature (25° C.). Further, DOTS recording medium is immune to chemical, water, and other environmental damage and is impervious to corrosion.
As described in U.S. Pat. No. 6,505,330, DOTS recording medium may be formed by coating an alloy of Antimony, Tin, and one or more additional metals onto a polymer film. The DOTS recording medium may be coated on the film using a physical vapor deposition (PVD) process such as, for example, DC magnetron sputtering. The film may be a dimensionally stable polymer material such as, for example, polyethylene terephthalate (PET), commercially known as Mylar® or Estar®. The DOTS recording medium may have a thickness of about 0.08 μm and may be protected by an SiOx overcoat of about 0.095 μm thickness.
In contrast to conventional magnetic tape, a PVD coating technique does not require chemical binders or solvents and yields strong adhesion between the recording material and the base film. Thus DOTS recording medium is believed to be relatively immune to mechanical failures such as delamination, chemical creep, fading, etc. suffered by conventional magnetic media over extended time periods.
Data may be written onto the DOTS recording medium by localized heating using a laser or other energy source. For example, U.S. Pat. No. 7,248,278 describes a printing system that may be suitable for writing data onto the DOTS recording medium. A linear spatial light modulator is illuminated by an expanded laser beam, and an image of the spatial light modulator is projected onto a photosensitive surface, which could be the DOTS recording medium.
Recorded data may be read from the DOTS recording medium by detecting the localized optical reflectivity of the media. For example, U.S. Pat. No. 5,321,683 describes a system for reading the DOTS recording medium. A line of data on the DOTS recording medium is illuminated by a linearly expanded laser beam, and an image of the DOTS recording medium is projected onto a detector array.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number where the element is introduced, and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.